In industrial, marine, commercial, laboratory and meteorological applications, it is often necessary to measure, read, record and transmit to remote locations readings of temperatures or pressures or variations thereof over a period of time. An instantaneous visual or electrical readout thereof may be required or, in other applications, it may be desirable to control the operation of other apparatus by the generation of an electrical or mechanical signal in response to changes in temperature or pressure. In certain well-known applications, changes in temperature or pressure induce physical motion within the sensing element, which is translated by a mechanical linkage to a needle or an indicator dial for an immediate visual readout. In other applications, rotary motion produced by a temperature or pressure sensing element is translated by a potentiometer or a shaft encoder into an electrical output signal. This signal may then be used to produce a visual readout of the temperature or pressure or it may be used to control other apparatus. In each of the above cited examples, a mechanical linkage is necessary to translate temperature or pressure variations sensed by an element into a visual mechanical movement or an electrical signal.
Electrical and visual signals have been generated directly without the use of unnecessary linkages in torque meters. Examples of these torque meters may be found in U.S. Pat. No. 4,166,383 and the prior art cited therein. Such torque meters produce a magnified output indicative of the movement of the shaft which in turn is a function of the torque applied thereto. Small movements of the shaft may be detected by relatively large movements of the axial marker provided thereon with respect to an aperture.
In many of the above-referenced applications, temperature or pressure measurements are made under conditions which require the instrument to withstand substantial vibrations, pressure pulsations, or physical impact. Most available instruments which are designed to withstand such abuses are expensive and have a heavy construction especially designed to protect the instrument against such harsh usage. Most of such temperature or pressure gauges of conventional dial and needle design are not suited to be read electrooptically. The sensitivity of such prior art devices may be increased only by increasing the size of the device itself or by amplifying the visual signal produced. If the sensing element and its attendant gauge is enlarged in order to increase the sensitivity of the gauge, it often becomes larger and heavier than desirable, and more subject to vibrations, pressure pulsations, and impact due to its large inertial masses. Such a device is often more expensive as well. If the gauge is reduced in size to overcome these problems, the mechanical or optical apparatus necessary to amplify the visual signal produced by the gauge often renders the gauge too complex and too vulnerable to damage for ordinary commercial, industrial, marine and other uses.